If wireless communication devices, e.g., user equipment devices (UEs), are proximately located to each other, they may be able to use a “direct mode” path for data communications through a link directly between them without routing of the communications through any eNodeB, signalling gateway (SGW)/packet data network gateway (PGW), or other network node, e.g., shown in FIG. 1. Proximately located communication devices may alternative have their communications “locally-routed” through a shared eNodeB or other network node, e.g., shown in FIG. 2. In conventional cellular communications between devices, the device communications are routed through one or more eNodeB(s) and SGW/PGW, e.g., shown in FIG. 3.
In device-to-device (D2D) communication, the source and the target devices are wireless devices, e.g., UEs, that communicate directly between each other through wireless links without relay through another UE or network node. Some of the potential advantages of D2D communication are off-loading traffic that would other pass through the cellular network, faster communication, lower latency communication, increased awareness of surrounding wireless devices of interest, e.g., which are running the same application, higher-quality links due to a shorter distance directly between the D2D devices, etc. Some appealing applications of D2D communications are video streaming, online gaming, media downloading, peer-to-peer (P2P), file sharing, etc.
A more detailed example reference system architecture for D2D operation is illustrated in FIG. 4. The system includes two UEs, Proximity Services (ProSe) applications performed by the UEs to provide D2D communication functionality, an Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) node that provides cellular communication services to the UEs, an Evolved Packet Core (EPC) node, a ProSe function performed by a network node to setup and control D2D communications between the UEs, and a ProSe application server.
Currently, in some D2D communication the communicating devices always transmit at full power. Such full power transmissions introduce high interference to other communicating devices and network nodes. Some other D2D communicating devices iteratively adapt their transmit power based on measurements of path losses between the devices. Unfortunately, in practice not much information is available about the path losses between devices involved in D2D communication and such iterative approaches can be slow to adapt transmit power.
In LTE, uplink (UL) power control controls the transmit power of the different UL physical channels to ensure that a desired quality is achieved at the serving BS receiver. In Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) the UL power control has both open loop components and closed loop components. The open loop UL power control is derived by the UE in every subframe based on the network-signaled parameters and estimated path loss or path gain. The closed loop UL power control is governed primarily by the transmit power control commands sent in each subframe (i.e. active subframe where transmission takes place) to the UE by the network. This causes the UE to control its transmission power based on both open loop estimation and Transmit Power Control (TPC) commands. This power control approach can be used for Physical Uplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH) and Sounding Reference Signal (SRS). The uplink transmitted power for RACH transmission is only based on the open loop component, i.e. path loss and network signaled parameters.
In general, the UL power control in E-UTRAN may be described asPX,c(i)=min{PCMAX,c(i),F(γ1,γ2,γ3, . . . )},
where PX,c(i) is the UE UL transmit power on channel/signal X in serving cell c in subframe i, PCMAX,c(i) is the configured UE transmit power defined in subframe i for serving cell c, and F(γ1, γ2, γ3, . . . ) is a function of multiple parameters (including path loss) which are specific for the channel/signal X, e.g., PUSCH, PUCCH, SRS, Physical Random Access Channel (PRACH).
Known approaches are typically pathloss-based, which are difficult to adapt for use in D2D communication since the pathloss between UEs and eNodeBs is difficult to use to estimate pathloss directly between two UEs, particularly in view of the common use of directed antennas and non-uniform antenna gains which affect pathloss. These approaches utilize an iterative approach for transmit power control, e.g., based on measuring total interference from environment, received signal strength, etc., that if adapted to D2D communications can require an unsatisfactory long time to constrain excessively high power D2D transmissions and during which time undesirable interference can be caused to other network nodes and/or UEs. Moreover, these approaches are not designed to power-control a transmitter for D2D when the two UEs are located in different cells. These approaches may also be more directed to point-to-point power control.
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.